by Noelle La Croix, DVM, Dip. ACVO
The Ophthalmic Examination – Part 2: The adnexa, orbit, and anterior segment
The previous article in this series discussed menace responses, pupillary light and dazzle reflexes in the ophthalmic examination of companion animals. The examination continues by evaluating the anterior segment of the eye in a standardized manner (Table 1).
It cannot be overemphasized that an ocular examination, like any physical examination, should be performed systemically. Routine evaluations of the eyes of all patients will also aid the practitioner in establishing what constitutes a “normal” eyelid, conjunctiva, cornea, anterior chamber, iris, or lens. The wide variability in what is considered “normal” can only be learned through repetition, and it is often difficult to correctly identify the atypical case.
After a patient’s facial symmetry and menace responses are established (see previous article) the rest of an ophthalmic examination continues within a darkened room. The size and position of each globe are evaluated for microphthalmos, buphthalmos, and/or strabismus. The eyes can be retroplused to discover orbital masses. The eyelid margins are examined next. Normal eyelids are smooth, with open (non-impacted) meibomian gland ducts, and they lack distichia. Any alopecia, erythema, or masses are also noted. The underside of each eyelid (at the palpebral conjunctiva) is examined for meibomian gland impaction and ectopic cilia. Touching the eyelids will also normally elicit their closure (the palpebral reflex).
Any ocular discharge appreciated is considered abnormal. A clear (serous) discharge is usually the result of an overproduction of tears. Serous discharges can be the result of ocular discomfort, a blockage in the nasolacrimal drainage system, or tear wicking associated with entropion, trichiasis, or distichia. A mucoid discharge is typically secondary to low tear production or conjunctival inflammation. A purulent discharge indicates an infection and the underlying cause needs to be determined.
The conjunctiva is then examined on all its anatomical surfaces (palpebral, bulbar, and nictitans). The conjunctiva of the palpebral and nictitans are typically a light pink in color, whereas the bulbar conjunctiva is usually translucent. Any nodules, chemosis, hemorrhage, masses, icterus, excessive hyperemia, or additional thickness in the conjunctiva is considered abnormal. The nictitans are also examined for gland prolapse and/or scrolled cartilage. The underside of the third eyelid is also examined for foreign bodies, especially if a corneal ulcer has been appreciated.
The sclera is examined next. A normal sclera is white in color (whiter than an animal’s teeth). Conjunctival disease can obscure the sclera making its examination difficult. There are two large isolated straight vortex veins within the sclera that extend ~ 3 mm behind the limbus to the conjunctival fornix. These vessels drain the ocular choroid. The presence of multiple injected straight scleral vessels extending from the limbus to the fornix indicates ocular pathology. Other abnormalities of the sclera include infiltrations of cells, thinning of the sclera, scleral masses, and hemorrhage.
A corneal examination follows. The normal cornea is clear and free of aberrant vasculature. Other anomalies that may be found within a pathologic cornea include cellular infiltrates, fat or calcium deposits, edema, pigmentation, foreign bodies, and fibrosis. Retroillumination (strong lighting reflecting from the tapetum back to the examiner) may help highlight these corneal irregularities.
The anterior chamber of the eye is examined next, but it can be difficult to appreciate irregularities without a slit lamp. Corneal pathology can also obscure the anterior chamber. The clearest views of the anterior chambers are obtained by facing a patient’s respective sides (i.e.; looking at animal’s right side into its right anterior chamber). Any flare (protein) or cells that are found within an anterior chamber are indicative of disease.
The ophthalmic examination continues with an inspection of each iris. The ability of both dogs and cats to fully constrict their irides can be lost with age. A persistently dilated pupil may also indicate glaucoma or optic neuritis. Animals with progressive retinal atrophy, or sudden acquired retinal degeneration, will usually show some pupillary constriction in response to strong lighting. Pilocarpine can be used to delineate between iris atrophy or synechiae: if an eye is visual, and the pupil does constrict in response to pilocarpine, then a neurological etiology is suspected. The irides should also be examined for any thickening, fixation, synechiae (anterior or posterior), hyperpigmentation, rubeosis iridis, atrophy, coloboma, hemorrhage, irregular colorization, masses, iridodonesis, and/or persistent pupillary membranes.
Lastly, the lenses are examined following pupillary dilation induced by tropicamide. Most of the lens can only be visualized through a fully dilated pupil. Opacities of the lens are abnormal and are most clearly appreciated through retroillumination. The edge of the lenses cannot be seen, even with full dilation, so the presence of an aphakic crescent (an area of the pupil where the lens is absent) indicates lens subluxation.
This article can serve as an methodical approach to the examinination of the anterior segment of the eye. The first step in any ocular diagnosis is a comprehensive examination in the hopes of determining underlying pathology. If you have any further questions on performing an ophthalmic examination, please consult with a veterinary ophthalmologist.
Noelle La Croix, DVM, Dip. ACVO
Veterinary Medical Center of Long Island
75 Sunrise Highway
West Islip, New York 11795
(631) 587-0800; fax (631) 587-2006